1 /**
2 * Copyright 2003-2007 Greg Luck
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package net.sf.ehcache;
18
19 import org.apache.commons.logging.Log;
20 import org.apache.commons.logging.LogFactory;
21
22 import java.io.Serializable;
23
24 /**
25 * An immutable Cache statistics implementation}
26 * <p/>
27 * This is like a value object, with the added ability to clear cache statistics on the cache.
28 * That ability does not survive any Serialization of this class. On deserialization the cache
29 * can be considered disconnected.
30 * <p/>
31 * The accuracy of these statistics are determined by the value of {#getStatisticsAccuracy()}
32 * at the time the statistic was computed. This can be changed by setting {@link Cache#setStatisticsAccuracy}.
33 * <p/>
34 * Because this class maintains a reference to an Ehcache, any references held to this class will precent the Ehcache
35 * from getting garbage collected.
36 * <p/>
37 * The {@link #STATISTICS_ACCURACY_BEST_EFFORT}, {@link #STATISTICS_ACCURACY_GUARANTEED} and {@link #STATISTICS_ACCURACY_NONE}
38 * constants have the same values as in JSR107.
39 *
40 * @author Greg Luck
41 * @version $Id: Statistics.java 512 2007-07-10 09:18:45Z gregluck $
42 */
43 public class Statistics implements Serializable {
44
45 /**
46 * Fast but not accurate setting.
47 */
48 public static final int STATISTICS_ACCURACY_NONE = 0;
49
50 /**
51 * Best efforts accuracy setting.
52 */
53 public static final int STATISTICS_ACCURACY_BEST_EFFORT = 1;
54
55 /**
56 * Guaranteed accuracy setting.
57 */
58 public static final int STATISTICS_ACCURACY_GUARANTEED = 2;
59
60 private static final Log LOG = LogFactory.getLog(Statistics.class.getName());
61
62 private static final long serialVersionUID = 3606940454221918725L;
63
64 private transient Ehcache cache;
65
66 private final int statisticsAccuracy;
67
68 private final long cacheHits;
69
70 private final long onDiskHits;
71
72 private final long inMemoryHits;
73
74 private final long misses;
75
76 private final long size;
77
78
79 /**
80 * Creates a new statistics object, associated with a Cache
81 *
82 * @param cache The cache that {@link #clearStatistics()} will call, if not disconnected
83 * @param statisticsAccuracy
84 * @param cacheHits
85 * @param onDiskHits
86 * @param inMemoryHits
87 * @param misses
88 * @param size
89 */
90 public Statistics(Ehcache cache, int statisticsAccuracy, long cacheHits, long onDiskHits, long inMemoryHits,
91 long misses, long size) {
92 this.statisticsAccuracy = statisticsAccuracy;
93 this.cacheHits = cacheHits;
94 this.onDiskHits = onDiskHits;
95 this.inMemoryHits = inMemoryHits;
96 this.misses = misses;
97 this.cache = cache;
98 this.size = size;
99 }
100
101 /**
102 * Clears the statistic counters to 0 for the associated Cache.
103 */
104 public void clearStatistics() {
105 if (cache == null) {
106 throw new IllegalStateException("This statistics object no longer references a Cache.");
107 }
108 try {
109 cache.clearStatistics();
110 } catch (IllegalStateException e) {
111 if (LOG.isDebugEnabled()) {
112 LOG.info("Ignoring call because " + e.getMessage());
113 }
114 }
115 }
116
117 /**
118 * The number of times a requested item was found in the cache.
119 *
120 * @return the number of times a requested item was found in the cache
121 */
122 public long getCacheHits() {
123 return cacheHits;
124 }
125
126 /**
127 * Number of times a requested item was found in the Memory Store.
128 *
129 * @return the number of times a requested item was found in memory
130 */
131 public long getInMemoryHits() {
132 return inMemoryHits;
133 }
134
135 /**
136 * Number of times a requested item was found in the Disk Store.
137 *
138 * @return the number of times a requested item was found on Disk, or 0 if there is no disk storage configured.
139 */
140 public long getOnDiskHits() {
141 return onDiskHits;
142 }
143
144 /**
145 * @return the number of times a requested element was not found in the cache
146 */
147 public long getCacheMisses() {
148 return misses;
149
150 }
151
152 /**
153 * Gets the number of elements stored in the cache. Caclulating this can be expensive. Accordingly,
154 * this method will return three different values, depending on the statistics accuracy setting.
155 * <h3>Best Effort Size</h3>
156 * This result is returned when the statistics accuracy setting is {@link Statistics#STATISTICS_ACCURACY_BEST_EFFORT}.
157 * <p/>
158 * The size is the number of {@link Element}s in the {@link net.sf.ehcache.store.MemoryStore} plus
159 * the number of {@link Element}s in the {@link net.sf.ehcache.store.DiskStore}.
160 * <p/>
161 * This number is the actual number of elements, including expired elements that have
162 * not been removed. Any duplicates between stores are accounted for.
163 * <p/>
164 * Expired elements are removed from the the memory store when
165 * getting an expired element, or when attempting to spool an expired element to
166 * disk.
167 * <p/>
168 * Expired elements are removed from the disk store when getting an expired element,
169 * or when the expiry thread runs, which is once every five minutes.
170 * <p/>
171 * <h3>Guaranteed Accuracy Size</h3>
172 * This result is returned when the statistics accuracy setting is {@link Statistics#STATISTICS_ACCURACY_GUARANTEED}.
173 * <p/>
174 * This method accounts for elements which might be expired or duplicated between stores. It take approximately
175 * 200ms per 1000 elements to execute.
176 * <h3>Fast but non-accurate Size</h3>
177 * This result is returned when the statistics accuracy setting is {@link #STATISTICS_ACCURACY_NONE}.
178 * <p/>
179 * The number given may contain expired elements. In addition if the DiskStore is used it may contain some double
180 * counting of elements. It takes 6ms for 1000 elements to execute. Time to execute is O(log n). 50,000 elements take
181 * 36ms.
182 *
183 * @return the number of elements in the ehcache, with a varying degree of accuracy, depending on accuracy setting.
184 */
185 public long getObjectCount() {
186 return size;
187 }
188
189 /**
190 * Accurately measuring statistics can be expensive. Returns the current accuracy setting.
191 *
192 * @return one of {@link #STATISTICS_ACCURACY_BEST_EFFORT}, {@link #STATISTICS_ACCURACY_GUARANTEED}, {@link #STATISTICS_ACCURACY_NONE}
193 */
194 public int getStatisticsAccuracy() {
195 return statisticsAccuracy;
196 }
197
198 /**
199 * Accurately measuring statistics can be expensive. Returns the current accuracy setting.
200 * @return a human readable description of the accuracy setting. One of "None", "Best Effort" or "Guaranteed".
201 */
202 public String getStatisticsAccuracyDescription() {
203 if (statisticsAccuracy == 0) {
204 return "None";
205 } else if (statisticsAccuracy == 1) {
206 return "Best Effort";
207 } else {
208 return "Guaranteed";
209 }
210 }
211
212 /**
213 * @return the name of the Ehcache, or null if a reference is no longer held to the cache,
214 * as, it would be after deserialization.
215 */
216 public String getAssociatedCacheName() {
217 if (cache != null) {
218 return cache.getName();
219 } else {
220 return null;
221 }
222 }
223
224 /**
225 * @return the name of the Ehcache, or null if a reference is no longer held to the cache,
226 * as, it would be after deserialization.
227 */
228 public Ehcache getAssociatedCache() {
229 if (cache != null) {
230 return cache;
231 } else {
232 return null;
233 }
234 }
235
236 /**
237 * Returns a {@link String} representation of the {@link Ehcache} statistics.
238 */
239 public final String toString() {
240 StringBuffer dump = new StringBuffer();
241
242 dump.append("[ ")
243 .append(" name = ").append(getAssociatedCacheName())
244 .append(" cacheHits = ").append(cacheHits)
245 .append(" onDiskHits = ").append(onDiskHits)
246 .append(" inMemoryHits = ").append(inMemoryHits)
247 .append(" misses = ").append(misses)
248 .append(" size = ").append(size)
249 .append(" ]");
250
251 return dump.toString();
252 }
253
254 }